Radio-phonograph oscillatoramplifier



April 10, 1951 A; E. HAYES, JR

RADIO-PHONOGRAPH OSCILLAI'OR-AMPLIFIER Filed March 13, 1947 gwue/w'fo'n ALBERT E. HAYES JR I the frequency deviations Patented Apr. 10, 1951 AMPLIFI Albert E. Hayes, Jr., Towson,

Md., assignor to Bendix Aviation Corporation, Towson, Md., a

corporation of Delaware Application March 13, 1947, Serial No. 734,313 2 Claims. (01. 179-10011) This invention is directed to a radio-phonograph combination. More specifically it is directed to a radio-phonograph combination wherein maximum use is made, in phonograph operation, of circuits which have hitherto been considered useful only for radio reception.

It has been proposed in the past to reproduce sound records, recorded in the well known amplitude variation manner, by converting the mechanical displacements produced during the recording process into a variable frequency deviation of a predetermined radio frequency carrier. The frequency modulated carrier energy is then subjected to a detection process for converting into corresponding amplitude variations, One of the most important advantages of this method is that a capacity pickup device can be employed with the variable frequency oscillator. This pickup device is highly economical compared to the relatively expensive types of electrical pickup devices employed in the usual conventional method of converting the sound vibrations into audio signal energy.

It is recognized, however, that arrangements of the character described are limited in their application because of the necessity of maintaining a high order of frequency stability of the frequency-modulated oscillator to prevent its drifting entirely out of the range of the associated detector circuit. This is furthercomplicated by the fact that installations of the type wherein pickup units of economical construction may be used to advantage do not lend themselves to the economical inclusion of oscillators of sufficient stability. This fact has tended to limit the use of the economical capacity type pickup to the detriment of the industry at large.

An arrangement for eliminating the shortcomings of prior-art capacitive phonograph pickups is disclosed in my copending application for United States Letters Patent, Serial N 0.660,- 944, now abandoned.

The object of this invention is to eliminate the need for a specific oscillator tube when using a capacitive phonograph pickup in a radio-phono- I graph combination.

The object of this invention is accomplished by a switching system whereby an amplifier tube and its associated circuits may be caused to function as a phonograph oscillator with a minimum of circuit deviation from conventional receiver design practice.

Other and further objects and advantages of this invention will be apparent from a consideration of the following detailed description. taken in connection with the accompanying'drawing,

the single figure of which is a schematic diagram of a circuit embodying the invention. It is tobe expressly understood, however, that neither the description nor the drawing is intended to define .source of voltage indicated +3. The control electrode M of the tube In is connectedthrough a series combination of the resonant secondary circuit 15 of an IL F. transformer l6 and a condenser I! to ground. The cathode l8 of the tube I0 is directly connected to the suppressor electrode thereof, andto ground through a parallel circuit comprising a condenser 20 and a resistor 2| The screen 22 is connected to the cathode [8 through a condenser 23 and to the source of volt-' age +13 through'a resistor 24.

The secondary winding 25 of the transformer I3 is connected, at one terminal thereof, to the anode 26 of .a second electron discharge tube 21, and, at the other terminal thereof, to :ground through a series combination of two resistors 28 and 29. The cathode 30 of the tube 2! is connected to the point of junction of the resistor 28 and 29. The junction of the winding 25 and the resistor 28 is connected to an output terminal 3| and to ground through a series circuit comprising a resistor 32 and a condenser 33. The cathode 30 of the tube 21 is additionally grounded through a series circuit comprising a condenser 35 and a resistor 34. A single pole double throw switch 31 has its arm 36 connected to the unrounded side of the condenser I1 and its fixed contacts A and B respectively connected to the ungrounded sides of the resistor 34 and the condenser 33.

A second single pole double throw switch 38 has its arm 39 connected to the movable element 40 of a capacitive phonograph pickup, and its fixed contacts A2 and B2, respectively, connected to the control electrode I4 and ground. A third single pole double throw switch 4| has its movable arm 42 connected to the fixed element 43 of the capacitive phonograph pickup, and its fixed contacts A3 and B3, respectively, connected to ing capacity between into service as bias supply the anode II and ground. A stylus 44, secured operatively to the movable element 40, cooperates with the convolution of a recorded track of a phonograph record 45.

In operation the switches 31, 38, and M are ganged so as to selectively contact the fixed contacts A1, :A2, and A3 or the contactshB fBz, and B; respectively. With the ganged switches in the B position it will be manifest that the operation is that of a conventional radio receiver wherein the tube In serves as an I. F. amplifier andtube 21 functions as a diode detector. Audio output is obtained at the terminal 3|, and AVC is applied to the tube [0 through the filter icomprising :the resistor 32 and the condenser -33.

With the ganged switches in position A, however, the capacitive pickup provides sufficient coupling between the anode H and the control electrode 14 to permit the tube It to operate as a tuned-plate tuned-grid. oscillator with the vary- .the electrodes .14 and .43 causing a variation in the-magnitude of thefeedback voltage under the influence-of the-motion of thestylus 44. A grid leak resisto1w34is brought Inasmuch as vibration in the capacity :between the pickup-elements andi43:causes a variation of the magnitude ofthe feedback, it will be manifest that the bias voltagedeveloped across the resistor 34 will have a correspondingly varying component. A series condenser .35 blocks the "D. C. component of this voltage, and the A. C.

component appears across the resistor 29 as an audio reproduction of the modulation on the record 45. The condenser I11 in parallel with the resistor 34 has a low impedance at the frequency generated by the oscillator, but a comparatively high impedance to the desired audio frequency signals and thus serves to eliminate any oscillator-frequency voltage which might otherwise appear across-'theresistor 29.

The variation :of the feedback voltage of the oscillator produces a considerable amplitude modulation of the output of the oscillator, and this output is applied to the diode detector tube 21 through the transformer 13. Upon detection the audio-frequency modulation appears across the diode load resistor 28. Thewvoltages across the resistors28 and 29are thus in series, and the output signal at the .terminal 3l :comprises the sum of thetwo' audio signals ,:and is then ready for the oscillator.

for amplification by the audio frequency amplifier of the receiver.

What is claimed is:

i. In combination, a radio frequency amplifier having input and output circuits, a network including an electro-mechanical transducer, switching means for connecting said network between said output and said input circuits in a regenerative sense, whereby said amplifier acts as an oscillator, a resistor, a second switching means ganged with the first named switching means and operative to connect the said resistor in the grid circuit of said amplifier as a gridleak-resistor when said network is connected, a detector, means coupling said output circuit to said detector and means combining additively the ;output';of-..said detector and the alternating voltage developed across said grid-leak resistor.

"2, In combination, a radio frequency amplifier having input and output circuits, a network including an electro-mechanical transducer, switching means for connecting said network between said output and said input circuits in a regenerative sense, whereby said amplifier acts as an oscillator, a resistor, a second switching means ganged with the first named switching means and operative to connect the said resistor in the grid circuit of said amplifier as a gridleak resistor when said-network is connected, a detector, means coupling said output circuit to said detector, a load resistor for'said detector, a third resistor serially connected with said load resistor,.means applying the alternating voltage developed across said grid-leak resistor to the junction of said serially connected resistors, and output terminals for said detector, said serially connected resistors being connected across said terminals.

ALBERT E. HAYES, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

